hello everyone, im a little new to Logo and was wondering if i could get some help with a little project im running.

to start,

i have a logo 12/24 connected with an AM2 RTD expansion that has a single PT100 sensor on it.

the logo is controlling 3 valves that are normally closed and open when power is applied to the relays. 

each valve is connected to a heat exchanger that has different temperature coolant flowing through them and im looking to program the system to automatically cycle between each valve once a target temperature has been reached in the system. the PT100 is located right on the outlet of where all three coolant circuits meet to measure system temp.

here is an example of what im looking for.

lets say valve 1 controls the cold side, valve two controls the ambient or closed loop, and the third valve controls the hot loop.

if i set a cold target temp of -10C and a hot target temp of 95C. the system should open valve 1 until the target temp of -10C is reached.

once there it should close valve 1 and open valve 2 for the ambient for 30 seconds.

after 30 seconds it closes valve 2 and opens valve 3 to heat the system until 95C is reached.

once 95C is reached it should close valve 3 and open valve 2 again for the ambient for 30 seconds.

after 30 seconds valve 2 is closed and from there the cycle repeats.

i have been able to get this cycle to work using on/off delay timers to have the system hold a valve open for however long it takes to reach the target temps. however, whenever i want to change the target time i need to sit there and time the system for however long it takes to reach the target temp. and adjust the timers accordingly. 

so having the system automatically cycle once the desired temperature is hit would make it alot easier and faster to edit the system as needed.

would really appreciate any help on this as i have been stumped on how to get it to work.

thanks in advance for your help!